I'm trying to transform these plots to functions, but I'm having a hard time figuring out a formulaic 2D->3D transformation on this type of mapping. They collapsed an axis flat on the abscissa, and have contour lines you need to trace to find the eta_bow value.
The only approach I have right now is to fit polynomials on the contour lines, and then I would have two sets of polynomial functions, the H_1/3 and 1/C_Delta^2. I would interpolate within the two sets, and then I would find the intersection between the interpolation of the set H_1/3 with the interpolation of the set 1/C_Delta^2. But before I proceed with that approach, I wanted to check if there were other [better] ways to extract functional data from this graph.
Edit: I think I might be complicating it a little too much. A simpler way would be to just make find the "x,y,z" values of the grid points, and do a surface interpolation. In this case, I would only use the graph reading to find the eta_bow, and I would have to manually read the H_1/3 and C_delta values.